Unit 2 Redox and Electrochemistry

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Unit 2 Notes

Redox Reactions

Isabel Bhuiyan

Monday March 3, 2015.


Oxidation-reduction reactions, or redox reactions, are chemical reactions where there is a loss and gain of electrons at once.

OXIDATION REACTION = loss of electrons
REDUCTION REACTION = gain of electrons

If an ATOM loses electrons, the atom is OXIDIZED.
If an ATOM gains electrons, the atom is REDUCED.

If a SUBSTANCE or OVERALL COMPOUND loses electrons, it is the REDUCING AGENT.
If a SUBSTANCE or OVERALL COMPOUND gain electrons, it is the OXIDIZING AGENT.

Rules to Determine Oxidation Numbers

  1. Elements = 0
  2. Monatomic ion = charge of the ion
  3. Algebraic sum of oxidation numbers in a neutral compound = 0
  4. Algebraic sum of oxidation numbers in a polyatomic ion = charge of the polyatomic ion
  5. Hydrogen = +1
    Hydrogen = -1 (in metal hydrides)
  6. Oxygen = -2
    Oxygen = -1 (in peroxides)
    Oxygen = +2 (with fluorine)
  7. Group 1 metals = +1
  8. Group 2 metals = +2
  9. Halogens = -1 (when second in formula)
  10. In non-metal combinations, the more electronegative atom has the negative oxidation number. The less electronegative atom has a positive oxidation number. The only exception is ammonia, NH3, where hydrogen is positive.
  11. In hydrocarbons, hydrogen = +1 even though it is second in the formula.

Homework


Resources

Balancing Redox Reactions Using Oxidation Numbers

March 3, 2015
Natasha Valenton
Balancing Using Oxidation Numbers
  1. Assign oxidation numbers to everything (above each atom)
  2. Identify species oxidized and reduced
  3. Balance the species oxidized between the reactant and the product side. Do the same for species reduced
  4. Determine the total loss and total gain
  5. Find the LCM between the total loss and gain, use this to balance the redox participants
  6. Balance everything else by inspection

Examples
Ex. 1)
#1 - Oxidation numbers
1.JPG
#2-4 - Identify which is oxidized and reduced, balance between reactant and product side, find total loss and total gain
2.JPG
#5 - Find LCM of 10 and 1 then apply to balance the redox participants
3.JPG
#6 - Balance I2 + 10 HNO3 --> 2 HIO3 + 10 NO2 + 5 H2O

Ex. 1)
#1 - Oxidation numbers
4.JPG
#2-4 - Identify which is oxidized and reduced, balance between reactant and product side, find total loss and total gain

5.JPG
#5 - Find LCM of 2 and 10 then apply to balance the redox participants
6.JPG
#6 - Balance *remember to add second Br2 and reduce
  • 10 HBr + 2 HBrO3 à 6 Br2 + 6 H2O
  • 5 HBr + HBrO3 -->3 Br2 + 3H2O

Homework:
  • Worksheet-Balancing Redox Reactions (front)
  • Alka-Seltzer 1 pg lab report due Mar. 5
  • Nomenclature Test Mar. 5 (Clinic)

Resources

Electrochemisty and Electrochemical Cells

Mashiat Khan

Friday, March 6, 2015


Electrochemistry is the study of chemical reactions that convert chemical energy to electrical energy

ELECTROCHEMICAL CELLS

This is an electrochemical cell, a device that continually converts chemical energy to electrical energy.
IMG_20150307_142515~2.jpg
An electrochemical cell contains:
  1. Electrodes (2): solid electrical conductors that allow electrons to flow through them; do not have to be metal (for example, graphite can be used as an electrode)
  2. Electrolyte: aqueous solution or paste that electrodes are submerged in; allow flow of ions (for example, the electrolyte in car batteries is sulfuric acid)
  3. Wires: connect the electrodes so electrons can flow

Electrochemicals cells must be connected externally (wires and electrodes) and internally (flow of ions), so if there are two different electrolytes, a salt bridge or porous cup must be used to allow the flow of ions and maintain electrical neutrality.
  • Salt Bridge: contains a salt solution; usually a group 1 nitrate or acetate
  • Porous Cup: one electrolyte goes into the cup and the cup is placed in the other; ions can flow through the cup

HOW DO ELECTRONS FLOW?

  • Oxidization always occurs at the anode; reduction always occurs at the cathode
  • Electrons always flow from anode to cathode
  • Potential Difference (Voltage) is the force that pushes electrons around the cell; different voltages are created by different electrodes
  • Current is the rate at which electrons flow

TYPES OF ELECTROCHEMICAL CELLS

Galvanic/Voltaic Cells

Electrolytic Cells
  • Uses energy released from a spontaneous redox reaction
  • Anode is the negative electrode; cathode is the positive electrode
  • Electrons flow from anode to cathode (negative to positive)
  • No power supply needed (for example, using a battery)
  • Uses energy released from a non-spontaneous redox reaction
  • Anode is the positive electrode; cathode is the negative electrode
  • Electrons flow from anode to cathode (positive to negative)
  • Power supply needed (for example, recharging a battery)

STANDARD CELL NOTATION

IMG_20150307_142744~2.jpg
  • Oxidization is written before reduction
  • Reactants are listed before products
  • Cell is considered a standard cell when ion concentrations are 1.0M

HOMEWORK

  • Read and take notes on pg 634-641
  • Do all practice problems on pg 641 and learning check questions on pg 641-642
  • Quiz on Tuesday (oxidization numbers and balancing equations)

RESOURCES

Electrochemistry Layered Curriculum

Mar. 10, 2015
Natasha Valenton

Oxidation Numbers and Balancing Redox Reactions Quiz was written.
ANSWERS
IMG_5501.JPG
Class was given rest of period to work on Electrochemistry Layered Curriculum.
Electrochemistry Layered Curriculum
  • C Layer
    • Focus on Corrosion, Electrolysis and Electroplating
    • Must obtain 20 points in Corrosion 10 points in Electrolysis and 20 in Electroplating. 50 points total over 3 days.
  • B Layer
    • On Wednesday Mar. 11, 2 electrodes will be given to you and your partner at random that will be used in the electrochemical cell lab
    • Lab will be conducted on Friday. 1 page lab report for Electrochemical Cells is found on wiki Lab Reports
    • Figure out which chemicals are need and check to see if it’s on King’s Chemical List Chemical Lists
    • Electrolyte can be from household items. If from kitchen, bring your own
Homework
  • Electrochemistry Layered Curriculum – C Layer
Resources

Electrochemistry Layered Curriculum

Thursday, March 12, 2015
Jackielyn Jabson

Lesson:
  • No lesson
  • Ms. Wilson was away (there was a supply teacher)
  • Work period for Electrochemistry Layered Curriculum assignment

Homework:
  • Complete C layer on the Electrochemistry Layered Curriculum sheet
  • Complete procedure for electrochemical cell lab (B layer) on the Electrochemistry Layered Curriculum sheet
  • Research the chemicals needed for your electrochemical cell lab (B layer) and select chemicals that are on the Chemical List (ensure it is not restricted)

Reminders:
  • C Layer of Electrochemistry Layered Curriculum assignment must be completed by Friday, March 13 (must obtain 20 points from corrosion, 10 points from electrolysis, 20 from electroplating)

Resources:
Brief Explanations of Major Concepts in Electrochemistry:
https://www.youtube.com/watch?v=IV4IUsholjg

Types of Electrochemical Cells:
http://www.s-cool.co.uk/a-level/chemistry/electrochemistry/revise-it/electrochemical-cells

Overview of Electrolysis:
http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/electrolysis/electrolysisrev1.shtml

Brief Explanation for Electroplating (includes interactive diagram):
http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/electrolysis/electrolysisrev2.shtml


Electrochemistry Layered Curriculum

Mashiat Khan

Friday, March 13, 2015


Today was a work period for the Electrochemistry Layered Curriculum.
Nomenclature test and redox reactions quiz was returned.

Layer C

  • Ms. Wilson will not be officially checking points
  • Be sure to know all the content as it is testable material
  • Recap: You need to know the content for 50 points in total; 20 from Electroplating, 20 from Corrosion and 10 from Electrolysis

Layer B

  • The lab was not conducted today, it is scheduled for next Wednesday
  • The lab procedure was worked on in partners
  • Three different lab set-ups are needed to measure the voltage between the electrodes you were given
  • King's Chemical List was consulted before choosing the chemicals needed for the designs and a list of chemicals was given to Ms. Wilson
  • You must figure out how to make about 150mL of 1M solution of your chosen chemicals
  • This will be a one page lab report found here

Schedule For Next Week

Monday
  • Starting the organic chemistry unit; interim reports will be handed out
Tuesday
  • Redox and Electrochemistry Unit Test
Wednesday
  • Electrochemical Cells Lab
Thursday
  • No school due to OSSLT

Homework

  • Complete all 50 points for C layer
  • Finish lab procedure for B layer
  • Read and take brief notes on page 8, 9, 15-21 *avoid reading about isomers*

Resources